Debt and Financing Costs - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015
Debt Instrument [Line Items]
Unsecured credit facility available to Company	$ 5,300,000,000
Line of credit facility, remaining borrowing capacity	2,700,000,000
Commercial paper program	5,000,000,000
Current debt outstanding	2,598,000,000
Australia [Member]
Debt Instrument [Line Items]
Revolving bank facility	300,000,000
Canada [Member]
Debt Instrument [Line Items]
Revolving bank facility	300,000,000
Revolving Credit Facility Due December 2015 [Member]
Debt Instrument [Line Items]
Unsecured credit facility available to Company	2,000,000,000
Credit facility maturity date	Dec. 31, 2015
Revolving Credit Facility Due August 2016 [Member]
Debt Instrument [Line Items]
Unsecured credit facility available to Company	1,000,000,000
Credit facility maturity date	Aug. 31, 2016
Revolving Credit Facility Due June 2018 [Member]
Debt Instrument [Line Items]
Unsecured credit facility available to Company	2,300,000,000
Credit facility maturity date	Jun. 30, 2018
Notes Payable, Other Payables [Member]
Debt Instrument [Line Items]
Period For Borrowing Funds	270 days
Credit Facility One [Member]
Debt Instrument [Line Items]
Revolving bank facility	2,000,000,000
Credit Facility Two [Member]
Debt Instrument [Line Items]
Revolving bank facility	1,700,000,000
Credit Facility Three [Member] | United States [Member]
Debt Instrument [Line Items]
Revolving bank facility	$ 1,000,000,000